THE LARVA AND PUPA OF CYTILUS ALTERNATUS SAY, WITH A KEY TO THE KNOWN GENERA OF NEARCTIC BYRRHID LARVAE (COLEOPTERA: BYRRHIDAE)

The larva and pupa of Cytilus alternatus Say are described and illustrated. Some ecological information is also reported. A key to the known genera of Nearctic byrrhid larvae is provided. Byrrhid larvae are poorly known in North America, and only four genera have been briefly described or illustrated: Amphicyrta, Byrrhus, Cytilus (however, the figures are based on material from Denmark), and Lioon (Kincaid 1900; Boving and Craighead 193 1; Chu 1949; Peterson 1960). All byrrhid larvae have mandibles with no mola or prostheca but with a large setose lobe at the base of the cutting edge. They also bear a large maxillary articulating area, a finger-like galea, a well-developed lacinia, a free labrum, a labium with distinct prementum, mentum and submentum as well as a gular plate. They lack an operculum or urogomphi. Cytilus larvae are recognized immediately by their unique hairy habitus, their C-shaped body, and by the slightly bifid apex of the mandible. Cytilus is a small genus with only two known species in North America (Arnett 1971): C. alternatus Say, a common boreal transcontinental species which occurs also in Europe, and C. nigrans Casey from Newfoundland. In this paper a key is provided for the identification of the four known genera of byrrhid larvae, and the larva and pupa of C. alternatus, which were reared to adult stage from field-collected larvae, are described and illustrated.